Aqueous release coating composition for pressure sensitive adhesives

ABSTRACT

This invention is directed to an article comprising a backing layer, at least one pressure sensitive adhesive layer, and an aqueous release coating layer, wherein the pressure sensitive adhesive layer is affixed to at least one side of the backing layer and the aqueous release coating layer comprises a polymer, preferably having acid functionality, and an aqueous solution or dispersion of an organic compound having at least one fatty acid ester and at least one quaternary amine. 
     A method of using a mixture of a polymer, preferably having acid functionality, and an aqueous solution or dispersion of an organic compound having at least one fatty acid ester and at least one quaternary amine as a release coating is also disclosed. 
     The aqueous release coating layer permits the pressure sensitive adhesive layer to be easily separated from the backing layer, even after storage for long durations and under extreme temperature and humidity conditions. The aqueous release coating does not migrate into the pressure sensitive adhesive layer and interfere with the adhesive properties of the pressure sensitive adhesive.

BACKGROUND OF THE INVENTION

This invention relates to an aqueous release coating composition forpressure sensitive adhesives.

Pressure sensitive adhesives have widespread use as bonding agents forfilms, foil, and paper for tapes, labels and decals. Films, foil, andpaper for tapes, labels and decals will be hereafter referred to as"backing". The adhesive may be coated onto one or both sides of thebacking. The side of the backing coated with adhesive will be referredto hereafter as the "adhesive-coated backing side".

In tapes, for example, the adhesive-coated backing is typically woundonto itself to form a roll where the adhesive-coated backing side is indirect contact with the upper surface of the continuous backing layer inthe roll which typically does not contain adhesive. The side of thebacking not coated with adhesive but coated with a material whichfunctions as a release agent will be referred to hereafter as the"release-coated backing side". In certain cases, both sides of thebacking may be coated with adhesive and a release-coat paper containinga separate backing and a release coating may be applied onto one or bothsides of these adhesive-coated backing sides. Hereinafter a backinghaving both sides coated with adhesive will be referred to as "doubleadhesive coated backing" and the side or sides which contain therelease-coat paper will be referred to as the "release-coated paperside." The adhesive must release cleanly from the release-coated backingside or release-coated paper side without causing damage or leaving anyadhesive residue on the release-coated backing side or release-coatedpaper side.

Forming rolls from the adhesive-coated backing imposes an additionalrequirement on the adhesive. The adhesive must have differentialaffinity for the two sides of the backing, such that the adhesivepreferentially adheres to the coated backing side with no subsequenttransfer to the uncoated backing side of the adjacent layer when thebacking is unrolled.

There are two methods which result in differential affinity of theadhesive towards the two sides of the backing--the primer coating methodand the release coating method. In the primer coating method, anadhesive is selected which does not adhere to the backing and a primercoat is used to make the adhesive bond to the backing. The primer coatis first applied to the backing and then the adhesive is applied ontothe primer coat. When the adhesive-coated backing is rolled, theadhesive on the adhesive-coated backing side contacts the backing sidewhich does not contain adhesive but does not adhere to it. Examples ofthis method are solvent-based natural rubber adhesives coated onunplasticized polyvinyl chloride film and aqueous-based acrylicadhesives coated on oriented polypropylene film where the coated backingside has been "primed" by corona discharge treatment.

In the release coating method, a release coat is applied to the backingside which does not contain adhesive ("release-coated backing side") andan adhesive is applied the opposite backing side ("adhesive-coatedbacking side"). The release coat has a strong affinity for the backingbut a weak affinity for the adhesive. Release coats are typically usedwith solvent-based natural rubber adhesives and hot-melt blockcopolymers coated on oriented polypropylene film.

Release coating may alternatively may be applied to a separate backingwhich is subsequently applied to the adhesive-coated side of the backing(hereinafter referred to as "release-coat paper.")

There are several requirements which a coating must meet to function asa release coating. It must exhibit low affinity toward the adhesive withwhich it will directly contact when the backing is wound into a roll.This low affinity must be maintained over time and under temperature andhumidity fluctuations and extremes. However, the release coating mustnot reduce the adhesive bonding between the backing and the adhesive tosuch an extent that the roll "telescopes." The release coating must alsostrongly bond to the backing side so that it does not delaminate whenaggressive adhesives are used. Further, components of the releasecoating must not migrate into the adhesive, thereby deteriorating theproperties of the adhesive.

It is also desirable for safety, health and environmental reasons to usea release coat which is aqueous and does not contain solvents.

SUMMARY OF THE INVENTION

This invention is directed to an article comprising a backing layer, atleast one pressure sensitive adhesive layer, and an aqueous releasecoating layer, wherein the pressure sensitive adhesive layer is affixedto at least one side of the backing layer and the aqueous releasecoating layer comprises a polymer, preferably having acid functionality,and an aqueous solution or dispersion of an organic compound having atleast one fatty acid ester and at least one quaternary amine.

This invention is also directed to a method of using a mixture of apolymer, preferably having acid functionality, and an aqueous solutionor dispersion of an organic compound having at least one fatty acidester and at least one quaternary amine as a release coating.

The aqueous release coating layer permits the pressure sensitiveadhesive layer to be easily separated from the backing layer, even afterstorage for long durations and under extreme temperature and humidityconditions. The aqueous release coating does not migrate into thepressure sensitive adhesive layer and interfere with the adhesiveproperties of the pressure sensitive adhesive.

DETAILED DESCRIPTION OF THE INVENTION

The pressure sensitive adhesive articles of this invention, such as forexamples tapes, films and labels, are composed of at least threecomponents:

(1) backing;

(2) pressure sensitive adhesive; and

(3) aqueous-based release coating

where either:

(1) the pressure sensitive adhesive is applied to one side of thebacking ("adhesive-coated backing side") and the release coat is appliedto the opposite side of the backing ("release-coated backing side"); or

(2) the pressure sensitive adhesive is applied to both sides of thebacking ("double adhesive-coated backing") and the release coating iscontained in release-coat paper which is subsequently applied to leastone adhesive-coated backing side.

The backings of this invention are conventional materials, such as forexample plastics including unplasticized polyvinyl chloride,polyethylene, polypropylene, polyester, and other substrates used inself-wound tapes; paper including crepe or flat paper and those used inmasking tapes; nonwovens including cellulosics; and the like. Typicallythe backing thickness is from about 20 μm to about 40 μm.

The pressure sensitive adhesives of this invention are conventionalmaterials, such as for example, aqueous acrylic adhesives; solvent-basedrubber adhesives including cis-1,4-polyisoprene; hot-melt blockcopolymer adhesives; synthetic rubbers including styrene-butadienerubber; and the like.

Applicants have discovered a novel pressure sensitive adhesive articlewhich contains a conventional backing material and a conventionalpressure sensitive adhesive with a novel release coating composition.The release coating composition useful in this invention must contain apolymer and an aqueous solution or dispersion of an organic compoundhaving at least one fatty acid ester and at least one quaternary amine.The organic compound having at least one fatty acid ester and at leastone quaternary amine is incorporated with the polymer at a level of fromabout 0.1% by dry weight to about 50% by dry weight, based on the dryweight of the polymer, preferably 1% by dry weight to about 10% by dryweight.

The release coating composition of this invention contains awater-soluble polymer, a latex polymer or a mixture thereof.

Examples of the water-soluble polymers include polyacrylates,polyacrylamides, polyvinyl alcohol, cellulosic polymers and the like.

"Latex" as used herein refers to a water-insoluble polymer which may beprepared by conventional polymerization techniques such as, for example,by emulsion polymerization. The latex polymer useful in the releasecoating composition may be prepared by emulsion polymerizationtechniques well known in the art.

A wide variety of monomers or mixture of monomers can be used to makethe latex polymer. For example, acrylic ester monomers, including methylacrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butylacrylate, isobutyl acrylate, secondary butyl acrylate, t-butyl acrylate,pentyl acrylate, neopentyl acrylate, hexyl acrylate, heptyl acrylate,octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, decylacrylate, isodecyl acrylate, lauryl acrylate, bornyl acrylate, isobornylacrylate, myristyl acrylate, pentadecyl acrylate, stearyl acrylate andthe like; methacrylic acid ester monomers, including methylmethacrylate, ethyl methacrylate, propyl methacrylate, isopropylmethacrylate, butyl methacrylate, isobutyl methacrylate, hexylmethacrylate, octyl methacrylate, isooctyl methacrylate, decylmethacrylate, isodecyl methacrylate, lauryl methacrylate, bornylmethacrylate, isobornyl methacrylate, myristyl methacrylate, pentadecylmethacrylate, stearyl methacrylate and the like; acrylic acid,methacrylic acid, itaconic acid, maleic acid, fumaric acid, styrene,substituted styrenes, butadiene, acrylonitrile, ethylene, vinyl acetate,acrylamide and the like may be used.

Preferably, the water-soluble polymer or a latex polymer useful in therelease coating composition of this invention contains acidfunctionality. The acid functionality may be incorporated in the polymerby incorporating acid-containing monomers into the polymer. Usefulacid-containing monomers include those monomers having carboxylic acidfunctionality, such as for example acrylic acid, methacrylic acid,itaconic acid, fumaric acid, citraconic acid; phospoethyl methacrylateand the like.

Preferably, the polymer useful in the release coating composition ofthis invention is nonionically stabilized. Suitable nonionic stabilizersinclude alkylphenoxypoly ethoxyethanols having alkyl groups of fromabout 7 to 18 carbons atoms and from about 6 to about 60 oxyethyleneunits, such as heptylphenoxypolyethoxyethanols,methyloctylphenoxypolyethoxy ethanols, and the like; polyethoxyethanolderivatives of methylene-linked alkyl phenol; sulfur-containing agentssuch as those made by condensing from about 6 to about 60 moles ofethylene oxide with nonyl mercaptan, dodecyl mercaptan, and the like, orwith alkylthiophenols wherein the alkyl groups contain from 6 to 16carbons atoms; ethylene oxide derivatives of long-chained carboxylicacids, such as lauric acid, myristic acid, palmitic acid, oleic acid,and the like, or mixtures of acids such as those found in tall oilcontaining from 6 to 60 oxyethylene units per molecule; analogousethylene condensates of long-chained alcohols such as octyl, decyl,lauryl, or cetyl alcohols, ethylene oxide derivatives of etherified oresterified polyhydroxy compounds having a hydrophobic hydrocarbon chain,such as sorbitan monostearate containing from 6 to 60 oxyethylene units;also, ethylene oxide sections combined with one or more hydrophobicpropylene oxide sections. Mixtures of alkyl benzenesulfonates andethoxylated alkylphenols may be employed.

Useful organic compounds having at least one fatty acid ester and atleast one quaternary amine include diglycerides and triglycerides with aquaternary amine functional group replacing one of the fatty acidgroups. Examples of these compounds include lecithin, hydroxylatedlecithin and lecithin derivatives, such as for example,phosphalidycholine and phosphatidylethanolamine, and the quaternaryammonium salt of tallow. Fatty hydroxylated, ethoxylated andpropoxylated quaternary and diquaternary amines are also useful in therelease coating composition of this invention. Many compounds arenaturally occurring. For example, lecithin is a naturally occurringmixture of phospholipids having both a hydrophilic portion and ahydrophobic portion and is found in most living cells. The primarysource of commercial lecithin comes from the soybean.

In addition, conventional coating components such as, for example,pigments, binders, vehicles, extenders, dispersants, surfactants,coalescents, wetting agents, rheology modifiers, thickeners, dryingretarders, antifoaming agents, colorants, waxes, preservatives, heatstabilizers, ultraviolet light absorbers and the like may be used in therelease coating of this invention.

The release coating may be applied to the backing by knife coating,roller coating and print coating. After the release coat is applied tothe flexible backing, it may be dried by heating. The dry weights of therelease coats which are useful in this invention are from about 0.01gram per square meter to about 10 grams per square meter according tothe selection of backing and pressure-sensitive adhesive and coatingtechnique. Dry weights of the release coats from about 0.1 gram persquare meter to about 2.0 grams per square meter are preferred.

The following examples are intended to illustrate the invention; theyare not intended to limit the invention as other applications of theinvention will be obvious to those of ordinary skill in the art.

EXAMPLE 1 Preparation of Release Coating Compositions

The release coating compositions were prepared by mixing together theingredients listed in Table 1. The release coatings were diluted to 35%solids with water for Release Coating 1 and 28% solids with water forRelease Coatings 2 and 3. The release coatings were then scrape-coatedonto 32 pound/ream crepe backing and dried for one minute at 275° F. togive an add-on of 3.5 pounds/ream.

                  TABLE 1                                                         ______________________________________                                                    Release    Release    Release                                     Ingredient  Coating 1  Coating 2  Coating 3                                   ______________________________________                                        Water        --         2.00 grams.sup.6                                                                         2.18 grams                                 Aqueous ammonium                                                                           --         0.30 grams                                                                               --                                         hydroxide                                                                     Lecithin    1.70 grams  --         --                                         (12.5% by weight                                                              in water).sup.1                                                               Tallow trimethyl                                                                           --         1.85 grams                                                                               1.85 grams                                 quaternary ammonium                                                           chloride salt                                                                 (27% by weight in                                                             water).sup.2                                                                  Acrylic latex                                                                             27.6 grams  --         --                                         polymer                                                                       (45.2% solids).sup.3                                                          Acrylic latex                                                                              --        13.59 grams.sup.6                                                                        13.59 grams.sup.6                           polymer                                                                       (46% solids).sup.4                                                            Water-soluble poly-                                                                        --         --         2.78 grams.sup.6                           mer (14% by                                                                   weight in water).sup.5                                                        Release coating                                                                           43.3%      38%        35%                                         solids                                                                        pH          8.5-9.0    8.5-9.0    8-9                                         ______________________________________                                         .sup.1 Dispersed Alcolec FF100 lecithin from American Lecithin Company  p     adjusted to 8.5-9 with ammonium hydroxide                                     .sup.2 Arquad T27W tallow trimethyl quaternary ammonium chloride salt fro     Akzo Chemicals, Inc.                                                          .sup.3 RES 68510 low surfactant, anionically stabilized acrylic latex wit     acid functionality from Rohm and Haas Company                                 .sup.4 RES 3112 nonionically stabilized acrylic latex without acid            functionality from Rohm and Haas Company                                      .sup.5 RES 86153 watersoluble polymer with acid functionality from Rohm       and Haas Company                                                              .sup.6 Premixed together before adding to latex polymer                  

EXAMPLE 2 Preparation of Test Specimens

The release coating compositions (Release Coatings 1, 2 and 3) wereevaluated to determine their effective in functioning as releasecoatings for pressure sensitive adhesives.

Adhesion Test Specimens

Strips (1 inch wide and 10 inches long) of commercial masking tape wereplaced with the pressure sensitive adhesive on the the release coatedside of the crepe backing prepared according to Example 1 to form thetest specimen. The excess backing was trimmed from the test specimen.The test specimen was then subjected to a 0.5 bar pressure to insurecomplete adhesion between the pressure sensitive adhesive of the maskingtape and the release coating on the crepe backing.

Test specimen were either prepared at room temperature and immediatelytested or prepared and aged for 3 days at 180° F. in a hot box tosimulate long term storage. Test specimens placed in the hot box wereweighted with a 1-inch metal bar to give 0.28 pounds/square inchpressure to simulate the pressure encountered in a roll of conventionaltape.

Readhesion Test Specimens

Strips (1 inch wide and 10 inches long) of commercial masking tape wereplaced with the pressure sensitive adhesive on the the release coatedside of the crepe backing prepared according to Example 1 to form thetest specimen. The excess backing was trimmed from the test specimen.The test specimen was then subjected to a 0.5 bar pressure to insurecomplete adhesion between the pressure sensitive adhesive of the maskingtape and the release coating on the crepe backing.

Test specimen were either prepared at room temperature and immediatelytested or prepared and aged for 3 days at 180° F. in a hot box tosimulate long term storage. Test specimens placed in the hot box wereweighted with a 1-inch metal bar to give 0.28 pounds/square inchpressure to simulate the pressure encountered in a roll of conventionaltape.

The masking tape portion was then manually separated from the releasedcoated portion. The masking tape was then placed on a stainless steelpanel in accordance with Pressure Sensitive Tape Council (PSTC)standards.

EXAMPLE 3 Adhesion Testing of Release Coating Compositions

The adhesion properties of the test specimens were evaluated using aT-peel test on an Instron Testing Machine (Model 1011). The T-peel testswere measured at room temperature at a rate of 12 inches/minute. Theresults are shown in Table 2.

                  TABLE 2                                                         ______________________________________                                                         Release (ounces/inch)                                                         Initial                                                                             Aged                                                   ______________________________________                                        Release Coating 1  7.9     9.6                                                Release Coating 2  5.7     12.3                                               Release Coating 3  8.4     12.2                                               ______________________________________                                    

Each of the release coatings performed well when tested immediatelyafter having been applied to the pressure sensitive adhesive as comparedto performance of typical pressure sensitive adhesives having no releasecoating applied. The increase in the release after aging for 3 days at180° F. in a hot box to simulate long term storage was also acceptable.

EXAMPLE 4 Readhesion Testing of Release Coating Compositions

The readhesion properties of the test specimens were evaluated using a180° Peel, a 90° Peel and a 90° Quik-Stick test in accordance withPressure Sensitive Tape Council (PSTC) standards. The results are shownin Table 3.

                  TABLE 3                                                         ______________________________________                                        Readhesion (ounces/inch)                                                      180° Peel                                                                             90° Peel                                                                           90° Quik-Stick                              Initial    Aged    Initial Aged  Initial                                                                             Aged                                   ______________________________________                                        Release                                                                              33.5    30.5    23.2  20.9  16.8  16.0                                 Coating 1                                                                     Release                                                                              29.3    26.2    19.0  18.0  11.1  10.1                                 Coating 2                                                                     Release                                                                              32.5    27.6    21.1  19.1  12.7  10.8                                 Coating 3                                                                     ______________________________________                                    

Each of the release coatings performed well when tested immediatelyafter having been applied to the pressure sensitive adhesive as comparedto performance of typical pressure sensitive adhesives having no releasecoating applied. The readhesion after aging for 3 days at 180° F. in ahot box to simulate long term storage showed an acceptable decreaseindicating that the release coatings did not substantially migrate intoand detrimentally affect the pressure sensitive adhesive's adhesion andreadhesion properties.

We claim:
 1. An article comprising a backing layer, at least onepressure sensitive adhesive layer, and an aqueous release coating layer,wherein said pressure sensitive adhesive layer is affixed to one side ofsaid backing layer and said aqueous release coating layer is provided onthe opposite side thereof, wherein said aqueous release coating layercomprises a polymer and an aqueous solution or dispersion of an organiccompound having at least one fatty acid ester and at least onequaternary amine, wherein said polymer prevents the migration of saidorganic compound into the adhesive layer.
 2. The article of claim 1wherein the polymer contains acid functionality.
 3. The article of claim2 wherein the acid functionality is carboxylic acid functionality. 4.The article of claim 1 wherein the organic compound is lecithin.
 5. Thearticle of claim 1 wherein the organic compound is an alkylestertrimethyl quaternary ammonium salt.
 6. The article of claim 5 whereinthe organic compound is a tallow trimethyl quaternary ammonium salt. 7.An article comprising a backing layer containing a pressure sensitiveadhesive layer affixed to each side of the backing layer and at leastone release coat paper layer in contact with the pressure sensitiveadhesive layer where the release coat paper layer comprises a polymerand an aqueous solution or dispersion of an organic compound having atleast one fatty acid ester and at least one quaternary amine, whereinsaid polymer prevents the migration of said organic compound into theadhesive layer.
 8. The article of claim 7 wherein the polymer containsacid functionality.
 9. The article of claim 8 wherein the acidfunctionality is carboxylic acid functionality.
 10. The article of claim7 wherein the organic compound is lecithin.
 11. The article of claim 7wherein the organic compound is an alkylester trimethyl quaternaryammonium salt.
 12. The article of claim 11 wherein the organic compoundis a tallow trimethyl quaternary ammonium salt.